The present invention relates in general to changeable plug, key operable padlocks, and more particularly to changeable padlocks of the exposed shackle type, having key lock plugs and a special slide cover for normally closing the cavity housing the key lock plug, permitting replacement of the key lock plug under certain conditions to adapt the padlock for use with a different key.
Heretofore, most key operated padlocks have ordinarily been constructed in such manner that the key lock plug is incorporated in the padlock body during manufacture so that it cannot be replaced without substantial destruction of the lock. However, it has been recognized that it is desirable in many instances, particularly in connection with high security padlocks adapted for warehouse or storage enclosures where constant security supervision is impractical or difficult, to provide for removal of the key lock plug in some manner so that a key plug designed for another key can be substituted to permit operation of the lock by a different key. Two basic types of changeable plug padlocks which have evolved are the bottom loading type, where a bottom plate serves as the removable cover for the plug cavity, and the top loading type, where a removable cover of some type is provided at the top of the padlock body. In the bottom loading type, such locks have been constructed so as to permit removal of the key lock plug either by use of a special change key, or by rotation of one or a pair of retaining screws accessible in the lower part of the socket or sockets for the padlock shackle legs, thus permitting change only when the lock is unlocked, or by retraction of a member accessible through one of the shackle leg sockets only when the associated shackle leg is withdrawn, to release the bottom cover plate. In such cases, the cover plate for the cylinder or plug cavity has been a bottom plate on the padlock body which is retained in position by some type of securing means which is operable only from the interior of the padlock body, but the presence of such a separate plate fixed on the padlock body provides for possibilities of removal of the bottom loading cover by wedges or similar attack tools. However, most previously available padlocks of the above described construction do not have sufficient resistance to attack to meet the requirements of high security lock applications, especially for protection of remote or intermittently supervised security closures.
More recently, high security key operable padlocks of the top loading type have been developed with removable top cover mechanisms for permitting changing of the key lock plug, as disclosed in U.S. Pats. Nos. 3,710,603 and 3,713,309, but it is desired to improve the operation of such padlocks for high security applications and provide locking mechanisms cooperative with the shackle legs to effectively resist strong shackle retracting forces.
An object of the present invention, therefore, is the provision of an improved key operable padlock construction wherein the key lock plug is protected from removal from a cavity therefor in the padlock body by a slidable cover which may be removed from the padlock case in a special manner when the shackle has been withdrawn to release position, thereby permitting substitution of a key lock plug designed for a different key.
Another object of the present invention is the provision of a novel key operable padlock wherein a slide type cover is normally held against movement from a protective position over the cavity housing the key lock plug by one of the legs of the padlock shackle and which is released for removal to a position permitting access to the key lock plug and its housing cavity for substitution of a different key lock plug when the shackle has been withdrawn to unlocking position and the key is positioned in a predetermined way.
In many uses of padlocks, the padlock is in an exposed position in remote, not continuously supervised, locations where a person seeking unauthorized entry into the space secured by the padlock may attempt to attack the padlock with attack tools such as wedges, sledge hammers, carbide tip saws, and other sophisticated devices to destroy the security of the lock. A further object of the present invention, therefore, is the provision of a novel key operable padlock construction for improving the security of padlocks designed to secure remote storage facilities and the like and enhance their resistance against efforts to gain unauthorized entry, wherein the locking mechanism for restraining the shackle within the padlock body and the slide cover for the cavity housing the key lock plug afford strong resistance to attack.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating preferred embodiments of the invention.